FIELD OF THE INVENTION
Compounds of this invention are analogues of natural prostaglandins.
Natural prostaglandins are 20 carbon atom alicyclic compounds related to prostanoic acid which has the following structure: ##STR1## By convention, the carbon atoms of I are numbered sequentially from the carboxylic carbon atoms. An important stereo-chemical feature of I is the trans-orientation of the side-chains C.sub.1 -C.sub.7 and C.sub.13 -C.sub.20. All natural prostaglandins have this orientation. In I, as elsewhere in this specification, a dashed line (---) indicates projection of a covalent bond below the plane of a reference carbon atom (alpha-configuration), while a wedged line ( ) represents direction above that plane (beta-configuration). Those conventions apply to all compounds subsequently discussed in this specification.
In one system of nomenclature suggested by N. A. Nelson (J. Med. Chem., 17: 911 (1972), prostaglandins are named as derivatives or modifications of the natural prostaglandins. In a second system, the I.U.P.A.C. (International Union of Pure and Applied Chemistry) system of nomenclature, prostaglandins are named as substituted heptanoic acids. Yet a third system of nomenclature is frequently used by those skilled in the prostaglandin art. In this third system (also described by Nelson), all prostaglandins are named as derivatives or modifications of prostanoic acid (structure I) or prostane (the hydrocarbon equivalent of structure I). This sytem is used by Chemical Abstracts and may become an I.U.P.A.C. accepted system.
Natural prostaglandins have the structures, ##STR2## in which: L and M may be ethylene or cis-vinylene radicals and the five-membered ring ##STR3##
Prostaglandins are classified according to the functional groups present in the five-membered ring and the presence of double bonds in the ring or chains. Prostaglandins of the A-class (PGA or prostaglandin A) are characterized by an oxo group at C.sub.9 and a double bond at C.sub.10 -C.sub.11 (.DELTA..sup.10,11); those of the B-class (PGB) have an oxo group at C.sub.9 and a double bond at C.sub.8 -C.sub.12 (.DELTA..sup.8,12); compounds of the C-class (PGC) contain an oxo group at C.sub.9 and a double bond at C.sub.11 -C.sub.12 (.DELTA..sup.11,12); members of the D-class (PGD) have an oxo group at C.sub.11 and an alpha-oriented hydroxy group at C.sub.9 ; prostaglandins of the E-class (PGE) have an oxo group at C.sub.9 and an alpha-oriented hydroxyl group at C.sub.11 ; and members of the F-class (PGF) have an alpha-directed hydroxyl group at C.sub.9 and an alpha-oriented hydroxyl group at C.sub.11. Within each of the A, B, C, D, E, and F classes of prostaglandins are three subclassifications based upon the presence of double bonds in the side-chains at C.sub.5 -C.sub.6, C.sub.13 -C.sub.14, or C.sub.17 -C.sub.18. The presence of a trans-unsaturated bond only at C.sub.13 -C.sub.14 is indicated by the subscript numeral 1; thus, for example, PGE.sub.1 (or prostaglandin E.sub.1) denotes a prostaglandin of the E-type (oxo group at C.sub.9 and an alpha-hydroxyl at C.sub.11) with a trans-double bond at C.sub.13 -C.sub.14. The presence of both a trans-double bond at C.sub.13 -C.sub.14 and a cis-double bond at C.sub.5 -C.sub.6 is denoted by the subscript numeral 2; for example, PGE.sub.2. Lastly, a trans-double bond at C.sub.13 -C.sub.14, a cis-double bond at C.sub.5 -C.sub.6 and a cis-double bond at C.sub.17 -C.sub.18 is indicated by the subscript numeral 3; for example, PGE.sub.3. The above notations apply to prostaglandins of the A, B, C, D, and F series as well, however, in the latter the alpha-orientation of the hydroxyl group at C.sub.9 is indicated by the subscript Greek letter .alpha. after the numerical subscript.
The three systems of nomenclature as they apply to natural PGF.sub.3.alpha. are shown below: ##STR4##